Electric tunnel kiln



Patented Nov. 1,v.1927. y l UNITED-STAT JAMES KELLEHER, OF CHIPPAWA, ONTARIO, CANADA, ASSIG-NOR TO HARPER ELEC- TRIO I FURNACE CORPORATION, A CORPORATION OF NEW YORK...

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ELECTRIC TUNNEL I KILN.

Application mea June 2s, i925. serial No.' 39,716.

This invention relates to electrically heated tunnel kilns. In firing many materials such as porcelain or other high-grade ceramic ware, the time during which the Aware is' 5 maintained at certain definite temperatures -nection withV the accompanying drawing vention.

wherein- Figz 1 represents ,diagrammatically in horizontal section a tunnel kiln provided with electricheating'elements arranged in accordance with one form' of myinvention.

Fig. 2 is a verticalv sectionof-such kilnl taken on ythe line 24-2 of Fig. 1.

Fig. 3 is 'a circuit diagram 'showing the, connections between the heater' resistors and a controlling rheostat.

Fig. 4 is a to plan vlew showing an yimi proved form 'o resistor which may be u tilized in certain cases in carrying out my 1nthe line5i'-`5 Fig. 5 isa section taken on of Fig. 4, and

:f lofFig. 4.

Fi v 6 is a-.section taken onthe line Referring to Figs.. land 2,'1 representstlie i body Vorbrickwork of the kiln 'and '2 the space through which the ware is'm'oved as itis being fired,v 3 and 4 represent resistors extending along .the length of the tunneland positioned in recesses in opposite sides't-hereof. vResistor fi's formed of two resistance ele'- ments, 7 andJ8,-connected in series at 10,

indicated in Figs. 1 and 3, while resistor 4 '1s ,formed of two reslstance elements, 5 and .6, 'which are` connected in series as shown .mf

Fig; 1. These resistance elements may con-- sist ofany material'which 'is'suitable for the dissipation of electrical energy and may con- Sisto-fone piece or two, three or four pieces,

arranged in multiplefor in series. As shown in Fig. 1, Ythe resistance elements' landl 6 are adapted 'to .be supplied" with currenty from '-niains 15 and 16 land theresistancenelements 7 and 8 are'adaptedtobe supplied'withcurrent from-mains 17 and 18. Regarding for simplicity the elements 7 and 8 and assuming that the ware is entering the fire zone from theleft in Fig. 1, this Ware will first pass resistor 8 and then'pass resistor7. As-

sumethat it' is desired ythat the ware attain a certain temperature by the time it has reached the end of4 resistor 8, and vhe maintained at that temperature duringits passage by the element 7. vIf both elements 7 and 8 had the same resistance. and both carried the 1 entire current from the mains'l7 and 18, the amount of energy dissipated in the elements 7 and 8 would be equal. As'the ware passes resistance element 8, sufiicient energy must be Vdissipated in element 8 to raise the ware up to the desired temperaturen' lIf after passing terminal 10 the energy dissipated at 7 is equal to that'at 8, the Ware will be raised to an even higher temperature than thaty requiredfbecause resistance element8 has already supplied the ware with the amount of energyrequired to raise it to the specified f temperature and therefore, merely to maintain the'ware at the temperature which it has attained by passing resistance element 8, the

energy dissipated.y in resistance element 7 must be only such as to take care of`losses through the furnace walls, convection, and in chemical-reactions in the ware, etc. In order to permit the use of two resistance elements in series, another small resistor, preferably made out of some resistance wire, is placed in-thevtunn'el of the kiln as shown at.21. This secondary orshunt resistor has a pluralitypf ytaps such as 22,23, 2 4, 425, 26. With one or another of these taps connected to v the point 9 at the outer'` end of resistance element 7 and another tap connected to the point 1i) between the elements 7 and 8, the current which passes vthrough main 18, terminal 11, resistance element 8, divides at the] terminal 10, onefportion passing through resistance element'7 and the remainder through terminal 10 line '19, one'of the taps such as 22 of resistor 21, a portion of resistor 21,-another ofthe taps of resistor 21 such as tap 25terminal 9, .to the main 17. In this manner a portion of vthe current is shunted around resistance `element .7 .and resistance element 7 carrying less current .than resistance element 8,the amount of ener ance element 7 is less t an that dissipated in 8. If the shunt'resistor or rheostat 21 were` 'placed outside. the furnace, the yfurnace los dissipatedin resistwould be inefficientbecause the energy dissi-A pated in rheostat 21 Would be Wasted. It is therefore placed inside the tunnel and may be utilized to heat up the Ware before 1t passes to the actual ring zone 7 and 8. p

Resistance elements 5 and 6 are connected in much the same manner as resistance elements 7 and 8, the difference being: that the resistance element 6 is shunted instead of the resistance element 5L- The connections as shown permit great flexibility in in controlling the temperatures at various parts of the tunnel' and permit a. control whereby the Ware is heated up gradually and then passed through a short hot zone to finish the Work of firing. It can be readily seen that the resistors or shunt rheostats27 and .2l might be placed on the outgoing side of the kiln so as to extend the hot Zone as the Ware cools off, for the purpose of anlnealing the Ware. It Will be'apparent that various changes may be made in certain cases in the arrangement and connections between the various resistors. l i

In certain cases I may lobtain a `desired variation in temperature at various points in the tunnel by employing a resistor such as is shown in Figs. 4, 5 and 6. This resistor` comprises two resistance elements 38and 39. connected in series, end to end at 35, and is preferably formedy o f bars of carbon'aceous material in which have been cut staggeredslots, as indicated at 37. The/.portionpf the resistor shown'at the left inTFi 4`-is of' high resistance and that at the right isv of low resistance, the. diiferencein` the resistvances being due to the spacing apart of the staggered slots. Figs. 5 and 6, which are.

fragmentary vertical longitudinal sections through the left and right hand portions of l the resistor respectively, show the cross-sec- -l tional areas ofthe current paths in these two portions of thevresistor'.

The system of dissipating energy of varying 'amounts may'utilize metallic resistors as -Wellas graphite or carbonaceons resistors. These resistors may`be round, cylindrical olnother forms'may beuse'd.`

I claim R 1. A tunnel kiln having an electric resisftor beaten locatedy in one portion of the tunnel, and means to control-the current through sald resistor comprising a resistor heater rheostat located in yanother 'portion -of the tunnel and adapted v to control the temperature ofsaid latter portion of-'the4 tunnel. I

2.' A` kiln having a tunnel through'which ware s"adapted to be passed, and means for heating the saine comprising` a resistance ele-fr ment extending along 'the tunnel, a second resistance element connected therewith'and extending along the tunnel at the rear of said first-named clement, and a resistor heater rheostat adapted to shunt said firstnamed element, said rheostat being located in said tunnell to the rear of said second# named element and adapted to control the.

shunt to one of said elements 4and adapted to control the temperature of said latter portion of the tunnel.

4. In a kiln having a which material to be heat-treated is adapted tunnel A through to be passed, a pairof heaterk resistance elements located at o ne part of the length of said tunnel, a second pair of heater resistl ance elements located behind said firstnal'ned pair, one element of one pair being electrically connected in series with one elementl of the otherpair, and ythe other ele-y ment of the one pair being electrically connected in series .with the other -element of the other, pair, a third pair of resistance elements located at another part of the length of said I tunnel, one element of said third pair being connected in shunt to 'an'element of said tirst pair and the other elementof said third pair being connected in shunt to an element of said second pair. y i l 5 In a kiln having'a tunnel through Which material to be heat-treated is adapted to b e passed, a `pair of heater resistance elements located at one part of the length ofsaid tunnel, a second pair of resistance elements located behind said tiret-named pair, one element of one pair being electrically connected 5 in series With one element of the other pair,"

and the other element of the one pair being electrically connected in series with the other elementbf'the other pair, a pair of 'rheo- `stats located in another part of said tunnel,-

one of. which is Aconnected in shunt to one element of the first pairk of resistance ele- Vsaid resistor comprising a resistor heater .rheostat located in a portion of the tunnel to "the rear Aof Isaid first named portion and adapted to controlthe temperature of the rear portion of said tunnel.

J AMES KELLEHER.. 

